Sewing machine for thermoplastic materials



y 1949. G. H. BROWN ET AL 2,477,040

SEWING MACHINE FOR THERMOPLASTIC MATERIALS Filed March 13, 1945 I N V ENTORS eorge HBrozan J3 ATTORNEY Patented July 26, 1949 SEWING MACHINE FORTHERMOPLASTIC MATERIAL George H. Brown and Rudolph A. Bierwirth,Princeton, N. 1., assignors to Radio Corporation of America, acorporation of Delaware Application March 13, 1945, Serial No. 582,564

6 Claims. 1

other or to intermediate layers of non-thermoplastic materials bybonding them together with the aid of heat and without the use ofthread. One of the forms of apparatus proposed heretofore for thispurpose, employs a Nichrome wire which'pierces the layers to be bondedtogether and is brought into contact with a metallic plate which closesan electrical circuit and causes a current to flow through the Nichromewire, thus heating the wire and the material close to the wire.

In apparatus of this type the wire will tend to bend when it buttsagainst the aforementioned me a lic plate and sparking at the point ofcontact burns the needle tip, rendering the needle tip blu t after a comaratively short period of use.

The p imary object of our present invention is to provide an improvedsewing machine of the type set forth above w ich will be free from theaforementioned difliculties.

More particularly, it is an object of our present invention to providean improved apparatus for and method of bonding together layers ofthermonlastic mater al in a quick and simple manner.

It is also an object of our present invention to prov de an improvedapparatus as above set fo th which can be applied readily to existing,convent onal Sewing machines which normally employ thread for sewing.

A further object of our present invention is to provide an improvedmethod and apparatus as aforesaid which will be highly eflicient in use.

In accordance with our present invention, we place around the needle ofa more or less conventional sewing machine an inductor coupling coilconnected to a source of radio frequency energy and induce in themetallic needle a high frequency current which rapidly heats the needleto a temperature suflicient to render plastic, in the region around theneedle, the layers of thermoplastic material to be sewn or bondedtogether. The heated, softened regions flow together and when the needleis withdrawn, these regions cool and the layers thus become bondedtogether. The inductor coupling coil is placed along the axis of theneedle either above or below the cloth or fabric to be sewn. Since theneedle is heated by induction, no electrical contact need be madethereto. This eliminates the sparking at the tip of the needle andgreatly increases its life. Moreover, since no electrical contact needbe made to the needle, the needle can be made quite flexible. Anadditional advantage afforded by our invention is that the needle may beheated at all times, even though it is reciprocating back and forth at agreat speed, wherefore it becomes a relatively simple matter to controlthe temperature thereof.

The novel features that we consider characteristic of our invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organ zat on and method of operation, aswell as additional objects and advanta es, thereof will best beunderstood from the following description of several embodimentsthereof. when read in connection with the accompanying drawing in whichFigure 1 is a front view of a portion of a sewing or bonding machine contructed in accordance with our present invention,

Figure 2 is a side elevation thereof shown partly in schematic form,

Figure 3 is a fragmentary, top plan view of a fabric having portionssewn or bonded together in accordance with our present invention,

Figure 4 is a view similar to Figure 2 but showing a modified form ofour invention,

Figure 5 is a front elevation of the apparatus shown in Figure 4, and

Figure 6 is a fragmentary, front elevation of still another form of ourinvention.

Referring more particularly to the drawing, wherein similar referencecharacters designate corresponding parts thoughout, there is shown, inFigures 1 and 2, two layers of fabric I and 3 of thermoplastic materialhaving overlapping portion la and Sawhich are to be bonded or sewntogether along a "seam" 5. This may be accomplished by placing thelayers l and 3 on the work plate I of a suitable sewing machine with theoverlapping portions la and 3a of the thermoplastic layers in the pathof a reciprocatory, steel needle 9. The needle is reciprocated by asuitable reciprocating bar i I carried by a head I3 and is arranged topass through a presser foot IS in known manner.

Surrounding the needle 9 is a coil or winding l1 having an axial boredisposed in the path of reciprocatory movement of the needle 9. The coill1 may be connected through a suitable transformer I! to a source ofradio frequency energy, such as a vacuum tube oscillation generator 2|.High frequency current supplied to the coil l1 induces a high frequencycurrent in the needle 9 and rapidly heats the reciprocating needle to atemperature sufficient to render the material I, 3 plastic. When theneedle 9 passes through or penetrates the overlapped layers la and 311,it heats the overlapped layers Ia and 3a and softens them in the regionimmediately therearound. These softened regions flow together into aunified region, and when the needle is withdrawn from the work, theunified region cools and the parts remain bonded together. A feed dog orany other suitable device l8 may be employed for advancing the sheets Iand 3 in known manner past the needle 9 with an intermittent motion, theneedle 9 piercing successive portions of the work during intervals ofstoppage thereof to provide a series of successive, bonded regions 23which form the seam 5.

The form of our invention shown in Figures 4 and 5 is quite similar tothat described above. However, instead of employing a multi-tum couplingcoil II, we may place around the needle 9 a single turn, conicalcoupling coil 21 of the type disclosed in Bierwirth Patent No.2,314,865. This type of coupling coil has the advantage of concentratingthe magnetic field established thereby in a small area along the axis ofthe coil and will therefore heat the needle very rapidly.

In both forms of the invention thus far described, the coupling coil isplaced above the work plate I and the fabric layers l and 3. If desired,one coil may be placed underneath the work plate 1, or two couplingcoils IT, "a may be provided, one above and the other below the workplate I, as shown in Fig. 6, it being sufficient merely that thereciprocating needle pass through one or more of such coils during itsreciprocatory motion and while it is pierced through the layers to bebonded together.

Although we have shown and described several forms of our invention, itwill undoubtedly be apparent to those skilled in the art that many othermodifications thereof are possible. Furthermore, it should be. apparentthat the present invention may be employed for bonding together not onlythermoplastic layers, but also textile fabrics impregnated withthermoplastic materials, textile or other fabrics interposed betweenlayers of thermoplastic materials, and the like. cases, it may bedesirable to make the pressure foot I! out of dielectric material toavoid inducing currents therein. Also, if desired, a switch 29 incircuit with the transformer l9 may be arranged under control of thepresser foot l5, so that current will be supplied to the heating coilsonly when the presser foot is lowered into engagement with the work.Various other changes are also possible within the spirit of ourinvention. We therefore desire that our invention shall not be limitedexcept insofar as is made necessary by the prior art and by the spiritof the appended claims.

We claim as our invention:

1. In apparatus for bonding together superposed layers of thermoplasticmaterial to form a seam, the combination of a metallic needle adapted topenetrate superposed layers of said material at points spaced from theedges thereof,

In some means for'inducing in said needle a high frequency electriccurrent adapted to rapidly heat said needle to a temperature sufflcientto render said material plastic in the region around said needle whensaid needle penetrates said layers, means for intermittently advancingsaid material with respect to said needle, and foricausing said needleto periodically penetrate said layers at spaced points along the lengthof said seam.

2. Apparatus according to claim 1 wherein said high frequency currentinducing means comprises an inductor coil surrounding said needle.

3. Apparatus according to claim 1 wherein said needle is arranged forreciprocatory movement along a definite path, and wherein said highfrequency current inducing means comprises an inductor coil having anaxial bore in said path through which said needle passes in the courseof its reciprocatory motion.

4. In a sewing machine, the combination with a work plate; a headthereabove; a reciprocatory, work-penetrable, metallic needle carried bysaid head; and a presser foot carried by said head in association withsaid needle for movement toward and away from said work plate of asource of high frequency electrical energy, an inductor coupling coilpositioned to have said needle pass therethrough during itsreciprocatory movement, means coupling said coil to said source, and aswitch in circuit with said means, said switch being coupled to saidpresser foot and being arranged to be closed when said presser foot islowered toward said work plate and opened when said presser foot israised from said work plate whereby energy will be supplied from saidsource to said coil only when said presser foot is lowered.

5. In apparatus for bonding together superposed layers of thermoplasticmaterial, the combination of a work plate having an opening thereinforsupporting the layers of material to be bonded together, a metallicneedle adapted to penetrate said layers and to pass through saidopening, means for inducing in said needle a high frequency electriccurrent adapted to rapidly heat said needle to a temperature sufiicientto render said layers plastic in the region around said needle when saidneedle penetrates said layers and passes through said opening, saidmeans comprising a pair of inductor coils one located above and theother beneath said work plate in alignment with said opening, and meansfor causing said needle to periodically penetrate said layers.

6. In apparatus for bonding together two layers of thermoplasticmaterial having only their edges overlapping so as to form a seam, thecombination of a metallic needle, means for reciprocating said needlealong a vertical axis, means for intermittently moving the overlappingedges of said material under said needle in a direction normal to theaxis of reciprocation, said movement taking place when said needle is ina raised position and said material being stationary when said needle isin its lowered position where it penetrates said material, a coil havinga central aperture and surrounding said needle at a point adjacent saidmaterial, and a source of radio frequency energy connected to said coilfor inducing heating currents in said needle whereby to raise itstemperature above the fusing temperature of said material.

GEORGE H. BROWN. RUDOLPHA. BIERWIRTH.

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